1. Field of the Invention
This invention relates to a damper that rotates to moderate rotational movement of a cover shifting between open and closed positions or the like.
2. Description of Related Art
Rotating dampers having a damping function of reducing rotational speed of piano key covers, toilet seats and the like are known, such as disclosed in Japanese unexamined patent publications No. Hei. 10-211025 (hereinafter referred to as “reference 1”) and No. Hei. 9-280290 (hereinafter referred to as “reference 2”).
The rotating damper, as described in the references, typically includes a rotating shaft provided in a cylindrical casing, divider walls that project from the inner peripheral surface of the casing toward the rotating shaft, and blades that project from the outer peripheral surface of the rotating shaft toward the inner peripheral surface of the casing. A valve body controls fluid flow between pressure chambers each defined by the divider wall and the blade.
More specifically, the valve body is operated to open and close a flow passage formed in the blade in accordance with a rotating direction of the rotating shaft in order to change fluid resistance based on the rotating direction. The rotating damper is structured such that the rotating shaft rotates at lower speeds when rotating in the direction that increases the fluid resistance. Therefore, the rotating damper is used in such a manner that fluid resistance decreases when the rotating shaft rotates in the direction that opens the piano key cover, the seat/seat cover or the like, and the fluid resistance increases when the rotating shaft rotates in the opposite direction, for example.
Among such rotating dampers are the ones disclosed in the referenced reference 1 and reference 2.
For example, the aforementioned rotating damper can be used for reducing a lowering speed of a toilet seat to cushion impact. However, recent mainstream toilet seats incorporate heaters, and are therefore heavy in weight. One possible way to reduce the lowering speed of the weighted toilet seat or other such objects, may be to increase the viscosity of the viscous fluid sealed in the casing of the rotating damper. Highly viscous fluid to be used can include, for example, highly viscous grease, crude rubber, clay or the like.
However, in structure of the damper described in reference 1, the valve body mounted on the blade repeats its bending movement in response to fluid pressure produced by rotation of the rotating shaft to open/close the flow passage. A problem arising in such structure having a valve body repeating bending movement is that the durability of the valve body cannot be guaranteed. In particular, when the rotating damper is filled with highly viscous fluid to provide higher torque, the valve body is placed under higher pressure, and therefore becomes more susceptible to damage. Hence, a damper in which the flow passage is adjusted by means of the bending movement of a valve body as described above is inadequate for use as high torque dampers.
On the other hand, in the damper described in reference literature 2, the valve body is mounted along the outer periphery of the rotating shaft and allowed to move in a circumferential direction. The valve body opens and closes the flow passage formed in the blade. This valve body does not incorporate repetitive bending movement in relation to fluid pressure, and therefore there is no problem of damaging at the bending portion of the valve body. However, in order to hold the valve body within its traveling range around the rotating shaft, another blade for holding the valve body is provided outside of the blade in which the flow passage is formed and flow in the flow passage is controlled by the valve body. In other words, the blade for holding the valve body is provided in the range of relative rotation of the rotating shaft and the casing.
In the rotating damper as described above, the rotation of the rotating shaft relative to the casing is limited by obstruction of the blade by the divider wall. For this reason, if the blade holding the valve body projects from the outer periphery of the rotating shaft as in the damper of reference literature 2, this reduces the rotating range of the rotating shaft. If such a damper is filled with highly viscous fluid for use as a high-torque damper, the thickness of the blade and/or the valve body must be increased in the circumferential direction in order to withstand high fluid resistance. As a result, a sufficient rotation angle may not be ensured. If the rotation angle is insufficient, problems may yet arise, such as the impossibility of retaining the opening state of the cover that stays in a horizontal position in the closing state.